A thickened or gelled electrolyte is less likely to leak from an electrochemical cell. Many materials have been used as thickening or gelling agents in the past. Such agents include soluble thickeners, insoluble absorbents such as starch, various cellulose type materials such as methyl cellulose, and some synthetic polymers.
A recurring problem with agents used heretofore has been that on standing or during cell discharge, liquid separated from many of the thickened solutions or gels. The liquid was then able to leak out of the cells. Further, during the manufacture of the cells and before the addition of the mixture to the cells, without constant agitation of the mixture, separation often occurred. This in turn resulted in the inaccurate addition of electrolyte due to the random ratios of liquid and gel being added to the cells. The inaccurate addition of electrolyte to the cells in many cases produced poor cells.
Increasing the quantity of agent added to the electrolyte sometimes reduced or prevented this separation, but it also decreased the volume and weight of active material in the cells. The greater quantity of gelling agent also generally decreased the ionic conductivity of the electrolyte which in turn increased the internal resistance of the cells.
Another drawback to the use of some known agents is that they were subject to chemical attack by the strong basic electrolyte solutions employed in alkaline type cells or the acid electrolyte employed in other types of cells. Similarly, some agents also attacked or were attacked by the various components of the cell. The decomposition products resulting from these reactions adversely affected the performance of many cells.
In some cells, a thickener was also added to the anode and/or cathode. Generally, the thickener was similar to that used for the electrolyte. The electrodes were gelled for many reasons depending on the type of cell involved and the results desired.
The use of water-insoluble or water absorbable agents such as those disclosed in U.S. patent application Ser. No. 106,996 filed on even date herewith have not only reduced the above enumerated problems but also unexpectedly improved the discharge capacity of the anode. These agents, even though improving the discharge capacity of cells made therewith do not consistantly form highly uniform gels.